Already known from prior art are rotating heat pumps or heat engines, in which a gaseous working medium is conducted in a closed thermodynamic cycle.
Described in WO 2009/015402 A1 is a heat pump or heat engine, in which the working medium in a pipe system of a rotor runs through a cycle involving the steps of a) compressing the working medium, b) dissipating the heat from the working medium by means of a heat exchanger, c) expanding the working medium and d) supplying heat to the working medium by means of an additional heat exchanger. The pressure of the working medium is increased or reduced through centrifugal acceleration, wherein the working medium flows radially outward in a compression unit and radially inward in an expansion unit relative to a rotational axis. Heat is dissipated from the working medium on a heat exchange medium of the heat exchanger in a section of the pipe system running axially or parallel to the rotational axis, to which section is allocated a co-rotating heat exchanger that exhibits the heat exchange medium. This device already enables an efficient conversion of mechanical energy and thermal energy of a low temperature into thermal energy of a higher temperature.
In practice, stringent requirements are placed on the stability of the device, which can be exposed to high centrifugal forces due to the rotational movement of the rotor.
In prior art, the heat exchangers were clamped in the area of the front ends of the heat exchangers. In this embodiment, the heat exchangers can disadvantageously bend at the ends between the clamps during operation, thereby detracting from the stability of the arrangement. In addition, operating safety can hereby not be ensured.
WO 98/30846 A1 discloses a generic rotor device for converting thermal energy. U.S. Pat. No. 3,846,302 describes another type of device for the thermal treatment of slurry. Finally, U.S. Pat. No. 3,258,197 relates to another type of cooling device.
By contrast, the object of the present invention is to provide a rotating device for converting thermal energy as indicated at the outset, which is capable of reliably withstanding high forces with the device in operation.
In the device according to the invention, this is achieved in that the rotor comprises a support body, which supports the inner and/or outer heat exchanger over its longitudinal extension, so as to retain the inner and/or outer heat exchanger.
The device according to the invention uses the centrifugal acceleration of the rotating system to generate various pressure or temperature levels; heat of a high temperature is here removed from or fed to the compressed working medium, and heat of a comparably low temperature is fed to or removed from the expanded working medium. Depending on the flowing direction of the working medium, the device is here optionally operated as a heat pump or engine. Use is here made of a heat exchanger positioned inwardly relative to the rotational axis and at least one heat exchanger positioned outwardly relative to the rotational axis, which are preferably situated essentially parallel to the rotational axis of the rotor. The inner heat exchanger is provided for heat exchange at a lower temperature, and the outer heat exchanger for heat exchange at a higher temperature. Several inner heat exchangers and several outer heat exchangers are preferably provided, which each are situated at the same radial distances to the rotational axis. According to the invention, the rotor comprises a support body, which supports the inner and/or outer heat exchangers over the length of the heat exchanger between the end faces against radial forces that arise during operation. In this embodiment, the rotor comprises a support body that supports the inner and/or outer heat exchanger over the length of the heat exchanger between the end faces against radial forces that arise during operation. The heat exchanger is advantageously supported by the support body essentially uniformly in the longitudinal direction of the heat exchanger, so that only slight or non-critical bends arise along the heat exchanger. All heat exchangers are preferably mounted to a shared support body, which is situated so as to rotate around the rotational axis as a constituent of the rotor. This makes it possible to achieve an especially stable design, with which the forces encountered during device operation can be absorbed. The support body can consist of one component or several components spaced apart in the longitudinal direction of the heat exchanger.
In order to keep the support body essentially at the temperature of the at least one inner heat exchanger during device operation, it is advantageous if the at least one outer heat exchanger comprises an insulating element comprised of a thermally insulating material between the outer pipe and support body, wherein the inner heat exchanger remains free of an insulating element. In order to keep the absolute temperature low, the outer or axially remote heat exchangers, which during normal operation comprise a higher relative temperature than the inner or axially proximate heat exchangers, can be thermally insulated from the supporting element in particular via tubular insulating elements having a significantly lower thermal conductivity by comparison to the support body. The thermally insulating material preferably exhibits a tensile strength of at least 10 Mpa, so as to prevent any flow under the load. In addition, the thermally insulating material shall comprise a temperature stability that corresponds to the maximum temperature of the heat exchanger. Therefore, it would be appropriate to use a conventional polycarbonate at operating temperatures of up to a max. 120° C. At higher temperatures of up to approx. 200° C., use can be made of polyether ether ketone, in particular with fillers such as carbon fiber or glass fiber, polyamide, in particular with various fillers, hard fiber materials or other high-temperature materials with a low thermal conductivity. Given the thermal insulation of the support body from the outer heat exchanger on the one hand at the absence of such an insulating element on the inner heat exchanger on the other hand, essentially the temperatures of the inner heat exchanger are relevant for the support body. As a result, advantageously slight losses in strength arise in the support body, if any. This comes to bear in particular when using aluminum or aluminum alloys, since they as a rule exhibit a declining strength starting at approx. 50°. Another advantage to this embodiment is that lower temperature gradients come about inside the support body, since the temperature of the axially proximate heat exchanger sets in essentially up until the insulating layer around the axially remote heat exchanger. This results in a lower residual stress in the support body. At especially high temperatures, however, it is also conceivable that both the axially remote and axially proximate heat exchanger be thermally insulated from the support body via insulating elements. In this case, the support body can be equipped with an active cooler (e.g., based on water cooling, thermal radiation or convection), so as to prevent losses in strength of the support body.
In a preferred embodiment, the support body is manufactured as a cast body, in particular out of aluminum, wherein high-strength aluminum alloys, for example AlCu4Ti, are preferably used. Given the high thermal conductivity of aluminum, it is advantageous to arrange the insulating element at least on the inner heat exchanger.
Alternatively, the support body can be fabricated out of (for example bainitic) cast iron. The low thermal conductivity eliminates the need for the insulating element of the axially remote heat exchanger given a support body manufactured in this way. The low declines in strength at higher temperatures make this support variant very well suited for high-temperature applications.
The support body can further be fabricated out of steel with the use of welded joints, wherein this embodiment brings with it in particular cost advantages at comparatively high strength properties. Another advantage to a welded support body is the nearly unlimited size scaling. Diameters of at least 4 m are here conceivable for the rotor. Another advantage to this variant is that the low thermal conductivity of steel eliminates the need for an insulating element on the outer heat exchanger.
In addition, the support body can be fabricated out of fiber composites, which advantageously are very lightweight and have a high stiffness.
Furthermore, the support body can be put together out of semi-finished products, wherein aluminum plates and aluminum pipes and/or steel plates and steel pipes can be used, for example. All materials available in the form of plates or pipes can here be used as the semi-finished product. One advantage to this embodiment lies in the fact that directly using semi-finished products makes it possible to largely prevent losses in strength, in particular without post-processing at a high temperature (for example, while welding).
In order to absorb centrifugal forces, it is beneficial if the support body comprises several plate elements situated essentially perpendicular to the rotational axis and spaced apart in the direction of the rotational axis, which plate elements have recesses for mounting the heat exchangers. The plate elements can comprise cutouts or depressions, so as to reduce the weight of the support body and/or alter the stiffness of the plate elements. This can advantageously be used to achieve uniform deformations during the transition to the edge region, which can comprise an elevated weight. The plate elements are preferably spaced apart at identical distances. The plate elements are preferably designed like discs. In this embodiment, the heat exchangers sag slightly between the plates due to the centrifugal acceleration, giving rise to additional bending stresses that must be absorbed by the heat exchanger. However, the advantage to this embodiment is that an elevated strength in the raw materials can be achieved by using semi-finished products for manufacturing purposes. In this embodiment, it is further advantageous if the exterior side of the heat exchanger comprises a support pipe, which comprises depressions in the peripheral direction for accommodating the plate elements. Shear forces can hereby advantageously be absorbed.
Provided as the support body in an alternative embodiment is a profile body extended in the direction of the rotational axis, which profile body comprises an inner element with at least one inner recess for the at least one inner heat exchanger, and at least one outer element with at least one outer recess for the at least one outer heat exchanger. Given an arrangement of at least two outer or two inner heat exchangers, the profile body has a rotationally symmetrical design relative to the rotational axis.
In order to absorb the forces, it is especially beneficial for the inner element and outer element to be joined together via connecting bridges running essentially in a radial direction.
In order to diminish or uniformly distribute the stresses in the profile body, it is advantageous to provide several outer elements, wherein preferably precisely two connecting bridges are provided between the inner element and each outer element. The connecting bridges are preferably arranged with the outer elements around the inner element in a star-shaped manner. In terms of force transmission, it is beneficial for the distance between the connecting bridges to continuously increase outwardly in a radial direction. Alternatively or additionally, the width of the connecting bridge can diminish outwardly in a radial direction.
To achieve an especially stable embodiment at a low material outlay, it is beneficial for the at least one outer element of the support body to be designed as a cylindrical receptacle for the outer heat exchanger. Alternatively, the receptacle can be inwardly partially open. Because the axially remote heat exchanger is not continuously supported, one core per heat exchanger can be omitted when casting. In addition, the introduction of force in the axially remote heat exchanger can be improved, making it possible to reduce the stresses emanating from centrifugal forces.
A preferred embodiment further provides that the support body comprises a cylindrical enclosure that surrounds the outer elements. The outer elements are here fastened to the interior side of the cylindrical enclosure. The cylindrical jacket tangibly reduces the frictional losses in the rotating operating state of the device. The rotor is preferably operated in a space with an ambient pressure of less than 50 mbar absolute pressure, in particular less than 5 mbar absolute pressure.